Integrated in-plane switching

ABSTRACT

This relates to adding multi-touch functionality to a display without the need of a separate multi-touch panel or layer overlaying the display. Instead, embodiments of the invention can advantageously utilize existing display circuitry to provide multi-touch functionality while adding relatively little circuitry that is specific to the multi-touch functionality. Thus, by sharing circuitry for the display and the multi-touch functionalities, embodiments of the invention can be implemented at a lower cost than the alternative of superimposing additional multi-touch related layers onto an existing display panel. Furthermore, since the display and multi-touch functionality can be implemented on the same circuit, they can be synchronized so that noise resulting from the display functionality does not detrimentally affect the multi-touch functionality and vice versa.

FIELD OF THE INVENTION

This relates to multi-touch panels in general and more specifically tointegrating multi-touch functionality in a display.

BACKGROUND OF THE INVENTION

U.S. patent application Ser. No. 11/483,008 filed on Jul. 6, 2006 andentitled “Capacitance Sensing Electrode with Integrated I/O Mechanism”(incorporated by reference herein in its entirety) teaches capacitancebased touch sensing. U.S. patent application Ser. No. 11/649,998 filedon Jan. 3, 2007 and entitled “Proximity and Multi-Touch Sensor Detectionand Demodulation” (also incorporated by reference herein in itsentirety) teaches a multi-touch sensing panel which can be combined witha display in a portable device. U.S. Provisional Patent Application Ser.Nos. 60/804,361 and 60/883,979, both entitled “Touch Screen LiquidCrystal Display” (and both incorporated by reference herein in theirentireties), show earlier designs for combining a multi-touch panelswith display panels.

It can be advantageous for a multi-touch panel to be combined with adisplay to form an integrated multi-touch display panel. Such a displaypanel can provide an intuitive interface to many types of devices.

Existing schemes to combine a multi-touch panel with a display caninvolve mounting a transparent multi-touch panel on top of a display.Alternatively, some existing systems can provide for a higher level ofintegration, wherein some layers of the multi-touch panel can also actas layers of a display. However, these systems can require that thecircuitry performing touch sensing be placed in different layers thancircuitry associated with the display functionality. This can result inrelatively expensive systems. Furthermore, the brightness of the displaycan be decreased, as the multi-touch related layers are usually notcompletely transparent.

SUMMARY OF THE INVENTION

This relates to adding multi-touch functionality to a display withoutthe need of a separate multi-touch panel or layer overlaying thedisplay. Instead, embodiments of the invention can advantageouslyutilize existing display circuitry to provide multi-touch functionalitywhile adding relatively little circuitry that is specific to themulti-touch functionality.

Thus, by sharing circuitry for the display and the multi-touchfunctionalities, embodiments of the invention can be implemented at alower cost than the alternative of superimposing additional multi-touchrelated layers onto an existing display panel. Furthermore, since thedisplay and multi-touch functionality can be implemented on the samecircuit, they can be synchronized so that noise resulting from thedisplay functionality does not detrimentally affect the multi-touchfunctionality and vice versa.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an existing in-plane switching (IPS) display.

FIG. 2 is a top view of an existing IPS display.

FIG. 3 is a top view of a multi-touch enabled display according to oneembodiment of this invention.

FIG. 4 is a schematic of an exemplary multi-touch enabled displayaccording to one embodiment of this invention.

FIG. 5 is a timing diagram of the operation of an exemplary multi-touchenabled display according to one embodiment of this invention.

FIG. 6 is a flow chart showing an exemplary method of operation duringthe touch scan mode according to one embodiment of this invention.

FIG. 7 includes several exemplary graphs illustrating the operation ofone embodiment of this invention.

FIG. 8 is a diagram showing an exemplary charge sensor and touchstimulus regions according to one embodiment of this invention.

FIG. 9 is a diagram showing an exemplary charge sensor, touch stimulusand guard regions according to one embodiment of this invention.

FIG. 10 includes two side views of an exemplary embodiment of theinvention which illustrate the purpose of guard regions.

FIG. 11 is a schematic of an exemplary multi-touch enabled displayaccording to one embodiment of this invention.

FIG. 12 is a diagram showing exemplary type A cells according to oneembodiment of this invention.

FIG. 13 is a diagram showing type B cells according to one embodiment ofthis invention.

FIG. 14 is a diagram of an exemplary touch sensing display according toone embodiment of this invention.

FIG. 15 is a flow chart showing a method of operation of one embodimentof this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following description of preferred embodiments, reference is madeto the accompanying drawings which form a part hereof, and in which itis shown by way of illustration specific embodiments in which theinvention can be practiced. It is to be understood that otherembodiments can be utilized and structural changes can be made withoutdeparting from the scope of the preferred embodiments of the invention.

This relates to adding multi-touch functionality to a display withoutthe need of a separate multi-touch panel or layer overlaying thedisplay. Instead, embodiments of the invention can advantageouslyutilize existing display circuitry to provide multi-touch functionalitywhile adding relatively little circuitry that is specific to themulti-touch functionality.

Thus, by sharing circuitry for the display and the multi-touchfunctionalities, embodiments of the invention can be implemented at alower cost than the alternative of superimposing additional multi-touchrelated layers onto an existing display panel. Furthermore, since thedisplay and multi-touch functionality can be implemented on the samecircuit, they can be synchronized so that noise resulting from thedisplay functionality does not detrimentally affect the multi-touchfunctionality and vice versa.

FIG. 1 is a side view of an existing in-plane switching (IPS) display.An in-plane switching display can be characterized by the fact that allcircuits associated with the display are placed within a singlesubstrate layer. Thus, for the display of FIG. 1, all circuits can beplaced within single thin film transistor (TFT) layer 100. While the TFTlayer can itself include several layers within it, the TFT layer isusually not itself divided to make space for any non-electronic layers(such as, e.g., liquid crystal layers, etc.)

A liquid crystal layer (layer 101) can be placed above the TFT layer.The liquid crystal layer can include a plurality of liquid crystals,such as liquid crystals 102. Color filter layer 103 can be placed abovethe liquid crystal layer. Plurality of electrodes 104 can be placedwithin the TFT layer. The electrodes can be selectively excited bycircuitry within the TFT layer. As a result, electric fields 105 canappear between various electrodes. The liquid crystals can bend as aresult of these fields. Due to the bending liquid crystals, the polarityof light 106 traveling across layers 100 and 101 can change. The lightcan be blocked or allowed to pass the color filter layer 103 dependingon its polarity. Therefore, the light that passes through the colorfilter layer (i.e. light 107) can be controlled by controlling thestates of the various electrodes 104. Thus, the functionality of anexemplary liquid crystal display can be realized.

FIG. 2 is a top view of an existing IPS display. The display can includea plurality of data lines, such as lines 201, 202 and 203. Various datalines can be associated with different colors. Furthermore, the screencan include a plurality of scan lines, such as scan lines 204 and 205.The scan lines are usually not directly connected to the data lines. Acell can be associated with an intersection of a scan line and a dataline. For example, cells 211, 212 and 213 can be associated with theintersection of scan line 204 with data lines 201, 202 and 203,respectively. Three cells associated with different colors can becombined to form a pixel.

Cell 211 is shown in additional detail. A transistor 205 can be placedin the cell so scan line 204 connects to the gate of the transistor,while data line 201 connects to its source. The drain of the transistorcan connect to electrode 206. Because of its shape, electrode 206 isoften referred to as a comb electrode. Electrode 207 (another combelectrode) can be placed in proximity to electrode 206 as shown. The twocomb electrodes can be placed in such a way so that their “teeth” are inproximity to each other, as shown. Electrode 207 can be connected to apredefined voltage, or ground through ground line 214. Alternatively,electrode 207 can be connected to the scanline for the next row 205.Electrode 206 can be excited, or driven by applying a voltagesimultaneously through scan line 204 and data line 201. For that reason,electrode 206 can also be referred to as the driven electrode, whileelectrode 207 can be referred to as the counter electrode. Drivingelectrode 206 can result in a voltage differential between drivenelectrode 206 and grounded (or set at a different voltage) counterelectrode 207. The voltage differential can create the lateral (i.e.,substantially parallel to the screen surface) fields which are used tocontrol the shape of the liquid crystals (see, e.g., liquid crystals 105of FIG. 1). Comb electrode structures similar to the one of cell 211 canbe provided for the other cells of the screen, including cells 212 and213. The comb structure may have horizontal “teeth” as shown, verticalteeth, diagonal teeth, or teeth having other shapes (such as zig-zagshaped teeth, for example). Embodiments of the current invention can becompatible with any of these comb design shapes.

Embodiments of the invention provide for modifying the above describeddisplay functionality in order to realize multi-touch functionality bythe same circuit. Accordingly, FIG. 3 shows an embodiment of theinvention in which the cells of FIG. 2 are modified so that they can beused to sense touching of the screen in addition to their usual displayrelated functions.

An additional line—counter data line 300—can be provided Like data lines201, 202 and 203, the counter data line can be vertical. Thus, it can beused for a plurality of pixels in a column, but each pixel in a row canbe associated with a single counter data line. Persons of skill in theart will recognize there can be other configurations of the counter dataline.

Similar to the other data lines, the counter data line can be connectedto scan line 204 through a transistor, such as transistor 301. The scanline can be connected to the gate of the transistor and the counter dataline to its source. A counter electrode line (line 302) can connect thedrain of the transistor to counter electrode 207 as well as all othercounter electrodes of the pixel (i.e., the counter electrodes associatedwith pixel cells 212 and 213). Therefore, while only cell 211 is shown,the other cells can be connected in a similar manner. It should be notedthat in some embodiments line 302 may not extend beyond a single pixelit is associated with. If the counter data line is connected to ground,the cells can operate in a manner similar to the ordinary displaycircuit of FIG. 2, because when the select line is excited, it can placetransistor 301 in conducting mode, which can result in all counterelectrodes being connected to ground (through the counter data line) asthey are in the circuit of FIG. 2.

FIG. 4 is a schematic of the circuit of FIG. 3. As it can be seen,counter electrode 207 can be connected to counter data line 300 throughtransistor 301, while driven electrode 206 can be connected to data line201 through transistor 205. Cells 212 and 213 can be similar to cell211, including transistors 403 and 404, respectively. Capacitor 400 canreflect the capacitance formed between the two comb electrodes (206 and207). Similarly, capacitors 401 and 402 can reflect capacitances formedin cells 212 and 213, respectively. A voltage appearing across any ofthe above capacitors can indicate a voltage difference between thedriven and counter electrodes. As discussed above, such a voltage cancause fields between the electrodes to control the liquid crystals. Inmost displays, a voltage appearing across the capacitors can indicatethat a light is being emitted by the display.

FIG. 5 shows a timing diagram of embodiments of the invention. As shownin FIG. 5, the screen can be interchangeably operated in LCD update 500and touch scan 501 modes. While in LCD update mode, the screen canperform ordinary display related operations. While in touch scan mode,the screen can be scanned to detect touch events on the screen'ssurface. The screen can switch between modes at a relatively highfrequency (e.g., 60 Hz) so that a human viewer may not be able todiscern any flicker as a result of the change of modes.

During the LCD update mode all counter data lines (such as line 300) canbe grounded (or alternatively set to a predefined voltage different fromthe voltage at which the driven electrodes are driven). This can resultin ordinary display related operation of the circuit (as noted above).

FIG. 6 is a flowchart showing a method of operating the above describedcircuit during the touch scan mode. At the beginning of a given touchscan period the cells can be discharged (step 600). More specifically,the capacitors formed by the driven and counter electrode (such ascapacitors 400, 401 and 402 of FIG. 4) can be discharged. This can beperformed by connecting the driven and counter electrodes to the samevoltage. For example, the driven and counter electrodes can both begrounded by (i) connecting all data lines including the counter dataline to ground, and (ii) exciting the scan line of a particular row ofcells (e.g., scan line 204). Thus, transistors 301, 205, 403 and 404 canall be placed in conducting mode and may, as a result, connect bothelectrodes of each capacitor to ground.

For most existing IPS LCD displays, the various cells can be excited ona row by row basis in order to implement the display functionality.Thus, a single row at a time can be excited by exciting its associatedscan line, after which another row is excited, etc. After being excitedthe cells within a row can hold a charge in the capacitor formed by thedriven and counter electrodes. That charge can affect the liquidcrystals associated with these cells, so that the color(s) these cellsare creating is preserved until the next time the scan line of aparticular row is excited.

According to embodiments of the invention, the discharge step 600 mayalso be performed on a row by row basis. FIG. 7 includes several graphsillustrating the timing of step 600 and other aspects of the operationof embodiments of the invention. Chart 700 indicates the timing of theexcitement of the various rows. The horizontal X-axis of chart 700 isassociated with time, while the vertical Y-axis is associated with therow of a display. Broken line 701 can indicate the state of a specificexemplary row, which will be referred to as row R. Solid lines 702-705can indicate an excitement of various select lines. In other words,every single point of any of lines 702-705 can indicate that the selectline associated with a particular row (indicated by the Y coordinate ofthe point) is in an excited state at a particular time (indicated by theX coordinate of the point).

Lines 702 and 704 can be parts of LCD write operations, while lines 703and 705 can be parts of pixel discharge operations. An LCD writeoperation can refer to exciting the driven electrode of a cell (and thusstoring charge in the capacitor formed by the two electrodes of a cell)in order to cause the display to display a color (as described above inconnection with FIG. 2). The discharge operation can be step 600 of FIG.6. In one embodiment, the LCD write and pixel discharge operations caneach last 3 ms, with a 5 ms period elapsing between each operation, asshown. In this case, each pixel can sustain the LCD voltage for 8 ms.After t=11 ms, the entire panel can be discharged, and touch sensing cancommence. Since the same color and counter data lines can be timemultiplexed between LCD operation and touch sensing operation, it can benecessary to wait for the entire panel to be discharged following LCDoperation, prior to the beginning of touch sensing. The stair-casewaveform 721 represents groups of LCD pixel rows being activated (i.e.,connected to their respective color and counter data lines by sending ahigh voltage through their respective select lines), so that touchsensing can operate as shown. In this example, touch sensing can operatebetween t=11 ms and t=16 ms. At t=16 ms, the cycle can repeat.

Graph 720 shows the voltage of the scan line associated with row R.Thus, graph 720 can show, for example, the voltage of scan line 204.Graph 730 shows the voltage differential between the driven and counterelectrodes in a cell of row R. In other words, graph 730 shows thevoltage across the capacitor formed by the two comb electrodes of thecell (e.g., capacitor 400 of FIG. 4).

At point 706, the LCD write operation can be performed on row R. Forthat purpose, the select line associated with that row can be placed ata high voltage for a short period of time (see point 706 at graph 720)and as a result a voltage difference can appear across the capacitor ofone or more cells in the row (see point 706 in graph 730). Betweenpoints 706 and 707, the capacitor can stay charged up, keeping a voltagedifferential between the comb electrodes and thus causing the variouspixels within the row to perform display functionality. Therefore theperiod between points 706 and 707 for row R can correspond to an LCDupdate period for that row (see, e.g., period 500 of FIG. 5).

At point 707, the LCD update period may end. At point 722, the row maybe connected to the columns for the purpose of touch sensing.

Touch sensing can be performed between t=11 ms and 16 ms. Thus, thisperiod can correspond to the period 501 of FIG. 5. By performing thedischarge step, some embodiments ensure that there is no voltage acrossthe comb electrodes of each cell in a row during the touch sensingperiod (as shown in graph 730) in order to avoid lighting any pixels inthe display as a byproduct of the touch sensing process. As noted above,a zero voltage differential between the comb electrodes usually causesno illumination in most existing IPS displays. In some embodiments,there can be an additional period 722 during which the voltage of theselect line can be high. This can be desirable because a high selectline voltage can be necessary to perform touch sensing functions (seemore detailed discussion below).

At point 708, an LCD write is performed again and the above discussedprocess repeats. In some embodiments, the voltage across the combelectrodes can be inverted every other LCD write step (as shown in graph730) by inverting the signals of the data lines.

Referring back to FIG. 6, after the cells have been discharged, theprocess can diverge for different cells based on the type of pixel eachcell belongs to. For the purposes of touch sensing, the various pixelscan be divided into two types—touch stimulus and charge sensor pixels.The type of each pixel can be predefined at the design stage or it canbe assigned by the device and configured as part of a set up operationor during normal operation.

FIG. 8 is a diagram of a group of pixels of different types. Pixels 800,802 and 804 can be touch stimulus pixels, while pixels 801 and 803 canbe charge sensor pixels. Each pixel can include several conductiveelements. More specifically, as noted above, each pixel can includethree cells, each cell including two comb electrodes. The pixels canalso include various conductive lines, such as portions of the data andscan lines. Consequently, capacitances can form between adjacent pixels.Thus, capacitances 805-809 can form between pairs of adjacent pixels asshown. The magnitudes of these capacitances can change if a user touchesone or more of the pixels, because a user's finger can affect theelectric fields between the conductors of adjacent pixels and thuschange the capacitance between these pixels. In practice, for someembodiments the capacitance between two pixels can decrease by about 10%as a result of a touching of a pixel

Thus, touch events on the screen can be measured by measuring anydecreases of the mutual capacitance of adjacent pixels. This measurementcan be performed by sending a stimulating signal to at least some of theelectrodes of one adjacent pixel (a touch stimulus pixel) and measuringthe charge of at least some of the electrodes of the other adjacentpixel. A more detailed explanation of using mutual capacitance to sensetouch events on a panel can be found in U.S. patent application Ser. No.11/649,998 discussed above.

For example, touch events in the proximity of pixel 801 can be detectedby sensing changes of capacitances 805 and 806. In some embodiments, thesum of these capacitances can be sensed. If the sum of the capacitancesis sensed, then touch sensing can be performed based on an areadifferent and larger than the actual pixel size. More specifically,touch sensing can be performed based on area 810, which encompasses theentire pixel 801 as well as the neighboring halves of pixels 800 and802. Area 810 indicates the area that if touched by a user can result ina significant change in the sum of capacitances 805 and 806. This areacan be referred to as a touch pixel and can be larger than a displaypixel. As shown in FIG. 8, the touch pixel can be the size of twodisplay pixels.

In other embodiments the touch pixel size can be even larger if, forexample, capacitances between pixel 801 and its vertical neighbors arealso measured. Furthermore, the touch pixel size can also be increasedby grouping several adjacent pixels into charge sensor and touchstimulus pixel regions. More specifically, elements 800-804 can each begroups of pixels instead of individual pixels. Thus, elements 800-804can be multi pixel charge sensor/touch stimulus regions. Pixels can begrouped vertically as well as horizontally. Thus, regions 800-804 caneach compose two rows and two columns of pixels.

In other embodiments, the touch pixel can be the size of, or evensmaller than a pixel. As shown in FIG. 2 a pixel can include multiplecells. In most embodiments a pixel is composed of three cells associatedwith the primary colors. While in the previous discussion each pixel wasconsidered as a whole for the purposes of touch sensing, in someembodiments the different cells of a pixel can be considered separatelyand can be individually (or in groups smaller than one pixel) designatedas charge sensor or touch stimulus cells. Thus, in some embodiments,elements 800-804 can refer to particular cells of a pixel, instead ofentire pixels or groups of pixels.

FIG. 6 shows how various pixels are reconfigured to serve the abovediscussed touch sensing roles. For touch stimulus pixels, some or all ofthe data lines of each pixel (including the counter data line) can bestimulated by being coupled to a stimulus signal (step 604). Thestimulus signal can be used to provide a stimulation which causes chargebuildup in charge sensor pixels in proximity to the touch stimuluspixels. In some embodiments the select lines associated with the touchstimulus pixel being stimulated (e.g., line 204) can be driven at highvoltage in order to place transistors 301, 205, 403 and 404 inconducting mode thus connecting the data lines to the comb electrodes.In some embodiments, it can be ensured that the signal applied to thecounter data lines is identical to signals applied to the various colordata lines. The color data lines can drive the driven electrodes of thevarious cells, while the counter data lines can drive the counterelectrodes of all cells of a pixel. Stimulating the counter and colordata lines with the same signal can ensure that pairs of driven andcounter electrodes are also stimulated with the same signal and novoltage differential occurs between the two electrodes. This can ensurethat no lighting of the display results as a byproduct of the touchsensing process.

For charge sensor pixels, some or all of the data lines of each pixel(optionally including the counter data line) can be coupled to one ormore charge amplifier circuits (step 602). The charge amplifier circuitscan be used to measure the charge present in at least some of theconductors of these pixels, and detect any changes of that chargebrought upon by changes of capacitance. In some embodiments the selectline associated with the charge sensor pixels being processed can bedriven at high voltage, in order to place transistors 301, 205, 403 and404 in conducting mode thus connecting the data lines to the combelectrodes.

At step 606, the charge at the current charge sensor pixel may bemeasured by the charge amplifier. The measured charge can indicate thecapacitance between the current charge sensor pixel and one or moreneighboring charge stimulus pixels. At step 608, the sensed capacitancemay be processed in order to determine whether or not the particularpixel is being touched. Processing can include demodulating a signalresulting from the charge amplifier, digitizing and/or averaging thissignal. Processing is discussed in more detail in the above mentionedU.S. patent application Ser. No. 11/649,998.

It should be noted that while the method of FIG. 6 refers to a chargeamplifier, another type of circuit can be used to sense capacitances.Also, while the method of FIG. 6 assumes that single pixels can be usedfor individual charge sensor and touch stimulus regions, as discussedabove, multiple pixels can be grouped to form single charge sensor andtouch stimulus regions. In other embodiments, a single pixel can includemore than one charge sensor and/or touch stimulus region.

A person skilled in the art would recognize that many of the abovediscussed embodiments can require the ability to drive multiple selectlines at the same time. This may be the case, for example, if the chargesensor/touch stimulus regions include multiple rows of pixels, or if thehigh select line periods (e.g., periods 721 of FIG. 7) of different rowsoverlap. Therefore, some embodiments of the invention may need to beconfigured so that multiple select lines can be driven at the same time(this is not the case for many existing LCD displays which only providethat one select line that may be high at a given time).

FIG. 9 shows another embodiment of the invention. In this embodiment, athird type of region—a guard region can also be present. Guard regionscan be placed between charge sensor and touch stimulus regions and usedto shield some electric fields between their neighboring regions. Thus,charge sensor region 902 can be separated from neighboring touchstimulus regions 900 and 904 by guard regions 901 and 903. Theconfiguration of FIG. 9 can result in touch pixel 905. Similar to thetouch stimulus/charge sensor regions, the guard regions can include oneor more pixels or one or more parts (cells) of a pixel. The guardregions need not be the same size as the touch stimulus/charge sensorregions. The guard regions can be configured during the touch scan modeby grounding all data lines and driving the select line(s) associatedwith these regions.

FIG. 10 includes two side views of an embodiment of the invention whichillustrate the purpose of guard regions. Diagram 1000 shows amulti-touch enabled display that does not feature any guard regions. ATFT layer 1006 of the multi-touch display can include at least one touchstimulus region 1004 and one charge sensor region 1003. A top layer 1001can be placed over the charge stimulus layer. The top layer can includeliquid crystals, filters, a cover glass, etc. A finger 1002 can bepressed against the top layer.

Without the finger, various electric fields, including fields 1006 and1005 can exist between regions 1004 and 1005. The fields can be causedby the capacitance between these two regions. When a finger is placedagainst the display, some of the fields—e.g., fields 1006—can be atleast partially removed or shunted by the finger. This can reduce thecapacitance between the two regions. However, fields 1005 may beunaffected by the finger. Therefore, the capacitance contributed byfields 1005 can remain even if a finger is present.

It may be desirable to maximize the fields (or the electromagnetic flux)that exist between the regions when no finger is pressing against theglass, but are removed or reduced by the presence of a finger. This canallow for a maximum difference in capacitance between “touch” and “notouch” events, thus allowing for easier detection of touch events.Therefore, it may be desirable to minimize the fields that are notaffected by the presence of a finger (i.e., fields 1005).

Diagram 1010 shows how guard regions can be used to reduce fields 1005.Diagram 1010 shows a configuration similar to that of diagram 1000, thatalso includes a guard region (region 1011) placed between regions 1004and 1005. The guard region need not affect desirable fields 1006.However, the guard region can block undesirable fields 1005. Since theguard region can include grounded conductors (e.g., the data lines andthe comb electrodes connected to the data lines) it can shield at leastsome of the fields that would have otherwise passed through it.

It should be noted that diagrams 1000 and 1010 may illustrate an idealresult. In practice, some of the undesirable flux represented by fields1005 can pass regardless of the existence of a guard region. However,even blocking some of the undesirable fields can prove beneficial forthe resolution of the overall system.

It should be noted that additional fields extending below the TFT layercan also exist. These fields are not shown in FIG. 10. According to someembodiments, these fields can be at least partially removed by placingconductors below the TFT layer.

FIG. 11 shows an exemplary schematic of a pixel and additional circuitryfor processing data at the counter and color (R, G, B) data linesaccording to some of the above discussed embodiments. It should be notedthat the additional circuitry can be common to all pixels that share thesame counter and color data lines (e.g., all pixels in the same columnas the pixel shown in FIG. 11). The counter data line can be connectedto a switch 1101. The color data lines can be connected to switches1102, 1103 and 1104, respectively. Different types of known switchingelements can be used for the switches, such as, e.g., solid stateswitches (e.g., transistor based switches) or microswitches. The first(leftmost) position of each switch can be connected to ground. Thecounter data line can be connected to ground when the pixel is in LCDupdate mode 500. Alternatively, during LCD update mode, the counter dataline can be connected to a programmed voltage that alternates betweentwo preset voltage values. This can facilitate generating voltagesacross the pixel that alternate in alternating frames, such as frameinversion, row inversion, or pixel inversion. Furthermore, all datalines can be connected to ground, or a predefined voltage, when thepixel is in touch scan mode 501, and the pixel is configured as part ofa guard region.

All data lines can be connected to driver circuit 1105 (the secondleftmost position of each switch) when the pixel is in the touch scanmode and the pixel is configured as part of a touch stimulus region. Thedriver circuit can be a circuit configured to provide a driver signal.The driver signal can be a sinusoidal signal, a square wave signal orany other type of signal that may be found suitable for touch sensingpurposes. All data lines can be connected to charge amplifier circuit1106 when the pixel is in the touch scan mode and configured to serve aspart of a charge sensor region. The charge amplifier circuit can be usedto sense the capacitance between the present pixel and one or moreneighboring charge stimulus pixels (e.g., capacitances 805, 806 of FIG.6). A signal processing circuit 1107 can also be provided to processdata produced by the charge amplifier circuit.

The color data lines (data lines 201, 202 and 203) can be connected todisplay data circuit 1108 (the rightmost position of their switches)when the pixel is in the LCD update mode. As noted above, in that modethe counter data line 300 can be connected to ground or to a voltagealternating between two preset voltage values to facilitate pixelvoltage inversion (frame inversion, row inversion or pixel inversion).

In some embodiments, a single driver circuit can be used for all pixels.The number of charge amplifier and signal processing circuits used candepend on the number of charge sensor regions on the screen. In oneembodiment, the charge sensor regions can be processed on a row by rowbasis, thus the number of charge amplifier and signal processingcircuits can be equal to the number of charge sensor regions in a givenrow. Accordingly, pixels that are in the same charge sensor region or indifferent charge sensor regions in the same column can be connected to asingle set of charge amplifier and signal processing circuits 1106 and1107. In other embodiments, there can be a set of charge amplifier andsignal processing circuits, for each column of charge sensor pixels, foreach charge sensor pixel, for each column of pixels or even for eachpixel.

In some embodiments, various pixels can be permanently designated ascharge sensor, touch stimulus or guard pixels. Therefore, some of thesepixels may not have as many possible states of their switches. Forexample, if a pixel is permanently designated as a touch stimulus pixel,switches 1101-1104 can lack an option for connecting to the chargeamplifier 1106. In other embodiments, the connections of FIG. 11 can bepreserved as to allow the touch scan mode roles of the various pixels tobe dynamically changed.

It should be noted that the above discussed embodiments can provide thatthe cells of the pixels are to be discharged upon entering the touchscan mode (see, e.g., step 600 of FIG. 6). Since the orientation of theliquid crystals depends on the voltage across the electrodes of thepixels, discharging the pixels during touch scan mode can affect theliquid crystals and may thus affect the color of the display. In someembodiments, the liquid crystal response time can be slower than thetouch scan mode period. Thus a pixel may not actually go dark during thetouch scan mode as a result of the discharge. However, as the averageor, more precisely, the root means square (RMS) voltage applied acrossthe electrodes of the pixel affects the position of the liquid crystalsand consequently the color of the pixel, the touch scan period canaffect the color of the pixel. Since the voltage across the electrodesof cells is zero during the touch scan period, this can reduce theaverage voltage and thus affect the color of the pixel (e.g., byreducing the brightness).

Consequently, in order to ensure that the color is the same as it wouldbe if no touch scanning were performed, the voltages with which thevarious pixels are excited during the LCD update (i.e., the voltagesapplied across the various color data lines during LCD update) can beincreased to compensate for the touch sense period and keep the RMS thesame as it would have been if there were no touch sense period. This canensure that performing touch sensing as discussed above does notnoticeably affect the display functionality. However, increasing thecolor data line voltages can result in higher power requirements for thedisplay.

FIGS. 12-15 show alternative embodiments of the invention which do notnecessarily require that the pixels be discharged during touch scanmode. Instead, the pixels can be kept at their original charge. Thus,higher power need not be used during the LCD update mode. Consequently,the embodiments of FIGS. 12-15 can be more efficient than the abovediscussed embodiments.

According to alternate embodiments of the invention, the cells of adisplay can be divided into two types—type A and type B. FIG. 12 shows aplurality of type A cells. These cells can be similar to the cells ofFIG. 2. The cells can include transistor 205 whose gate can be connectedto select line 204 and whose source can be connected to color data line201. The drain of the transistor can be connected to driven combelectrode 206 which is placed in proximity to counter comb electrode207. A capacitance 400 can exist between the electrodes. Thiscapacitance can be composed of the liquid crystal capacitance as well asan extra storage capacitor that can be created using parallel plates inthe metal layers of the TFT (a common practice in existing IPS LCDdisplays). The cells of FIG. 12 can be distinguished from those of FIG.2 in that additional common row 1200 and common column 1201 lines can beprovided. Counter electrodes 207 of the type A cells can be connected tothe common column lines (lines 1201). As can be seen, the common columnlines can be unused for the type A cells. While FIG. 12 illustrates a1:1:1 ratio between display pixels to common column lines to common rowlines, other ratios are possible, such as 3:1:1 or 3:3:1 or 3:1:3. Theuse of a higher ratio of display pixels to common lines can minimize theaperture ratio loss associated with the extra common lines.

FIG. 13 is a diagram showing a plurality of type B cells. The type Bcells can be similar to the type A ones with the distinction that thecounter electrodes are connected to the common row lines (lines 1200)instead. In addition, the type B cells can be designed to provide anequal aperture ratio as the A cells, so that the optical displayperformance is indistinguishable between A and B cells. This can ensurethat there is no display artifact associated with the differencesbetween type A and type B cells.

FIG. 14 is a diagram of an exemplary display. The cells in the displaycan be grouped into touch pixels, such as touch pixel 1403. As discussedabove, the touch pixels can include one or more cells and/or one or moredisplay pixels. The cells and/or pixels included in a touch pixel can bepositioned in single or multiple adjacent rows and/or columns. The touchpixels of the display can be divided into type A regions 1401 and type Bregions 1402. In some embodiments the divisions can be made based onvertical stripes, as shown. The number of touch pixels of the displaycan be different than shown.

According to one embodiment, each type A or B region can be a rectanglewith a height twice the size of its width. Thus, for example, the widthcan be 2.5 mm and the height can be 5 mm. Since the embodiments of FIG.14 can sense touch events by using a combination of type A and type Bpixels, the size of a touch pixel may be about twice the width of anindividual type A or B region (this is similar to the setup ofembodiments discussed in connection with FIG. 8). Therefore, using theabove discussed sizes can result in square touch pixels.

The various common row and common column lines can be sent throughbusses 1404 and 1405 to a touch sensing circuit 1406. The touch sensingcircuit can also be connected to the data lines of the display (notshown). An advantage of the stripe based positioning of the type A andtype B regions, can be that half of the common column lines need not beconnected to the touch sensing circuit as they are associated with typeB touch pixels only. In fact, in some embodiments, the common columnlines that are only associated with type B pixels can be entirelyremoved from the circuit.

FIG. 15 is a flowchart showing a method of operation of embodiments ofthe invention of the type shown in FIGS. 12-14. At step 1500, an LCDupdate may be performed. In this step, the touch sensing circuit canconnect all common row and column lines to ground. Since both the commonrow and column lines are connected to ground, the counter electrode ofeach cell (regardless of whether it is of type A or type B) can be alsoconnected to ground. Therefore, each cell can be configured in a mannersimilar to the cells of FIG. 2. Thus, during step 1500, the display canoperate in a manner similar to that of ordinary LCD displays. In someembodiments, step 1500 can take about 12 ms.

At step 1502, the display can switch from LCD update mode 500 to touchscan mode 501 (see FIG. 5). However, as opposed to the previouslydiscussed embodiments, no discharge of the pixels needs to be performed.Thus, all pixels and cells within them can be allowed to keep theircurrent internal charge (the charge being held by the capacitors formedbetween the driven and counter electrodes of each cell). At step 1502,touch pixels of type A can be driven with a stimulus signal. Thestimulus signal can be a signal oscillating around 0V. For example, thestimulus signal can be a 5V peak to peak sine wave signal oscillatingaround 0V. The touch pixels of type A can be driven by driving thecommon column lines associated with these touch pixels.

The touch pixels of type B can be connected to charge amplifiers orsimilar circuits designed to sense the charge at these touch pixels.This may be done by connecting the common row lines associated withthese touch pixels to the charge amplifiers. The outputs of the chargeamplifiers can be processed to sense changes of capacitance between atouch pixel of type B and a neighboring stimulated touch pixel of typeA. Such changes can signify touch events. Thus, during step 1502, touchevents can be detected based on measurements obtained from pixels oftype B. In some embodiments, step 1502 can last about 2 ms.

Step 1504 may be similar to step 1502 but the roles of touch pixels oftypes A and B may be reversed. In other words, during step 1504, thetouch pixels of type B can be stimulated (by driving the common rowlines), while the touch pixels of type A can be connected to chargeamplifiers in order to detect touch events (by connecting the commoncolumn lines to the charge amplifiers). In some embodiments, step 1504can also last 2 ms. After step 1504 is completed, a single touch scan ofthe display may be completed, and the process may proceed back to step1500 in which the display changes back to LCD update mode.

According to some embodiments, the select lines may not be excitedduring the touch sensing mode (i.e., steps 1502 and 1504). Thus thevarious transistors of the cells (e.g. transistor 205) can be left in anon-conducting state. Therefore, the data lines can be disconnected fromthe various cells during touch sensing. Thus, in ideal conditions, thestate of the data lines can be irrelevant during touch sensing. However,in practice the state of the data lines can affect the cells duringtouch sensing due to a capacitance across transistor 205. In someembodiments, all data lines can be grounded during steps 1502 and 1504.Consequently, any effect the data lines have on the cells can be keptroughly symmetrical for different cells, thus avoiding any visibleartifacts caused by data line interference.

As noted above, the later discussed embodiments can be performed withoutdischarging the cells. Thus, the various cells and display pixels can beemitting light while touch scanning is performed. Therefore, it may beimportant to ensure that the touch scan process does not causesignificant changes in the voltages across the comb electrodes of thevarious cells, thus causing undesirable visual artifacts.

If a given cell of either type is connected to a stimulus signal, thenthe common line (common column line for cells of type A or common rowline for cells of type B) can send the stimulus signal into the cell.The common line can excite the common electrode with a stimulus signal.The given cell can be lit, i.e., there can be an existing voltagebetween the driven and counter electrodes signifying that the cell iscurrently producing light. Since the TFT switch is open (i.e.,non-conducting), and there is a storage capacitance Cst at each pixelbetween the counter electrode and the data electrodes, then, in idealconditions, applying the stimulus signal as part of step 1502 or 1504should not change the voltage between the electrodes. In other words thecommon mode voltage of both electrodes may be modulating, due to thecommon line being driven, and Cst of the pixel, however because the TFTswitch is open, then the Cst can hold the same differential voltageacross the two electrodes, so that there is no change to the field seenby the liquid crystal.

However, the conditions of operation may differ from the ideal.Specifically, parasitic capacitance at transistor 205 can affect thevoltage changes of the driven electrode that result from the stimulationsignal so that they are not identical to those of the counter electrode.Therefore, a slight artifact, or a change of color can occur for regionsof the type that is currently being stimulated. In order to make thisartifact unnoticeable, steps 1502 and 1504 can be performed in quicksuccession, thus changing the regions that are being stimulated and atwhich the artifact appears. Since the human eye may not be able todiscern such a quick switch of the stimulated regions, if the artifactis noticeable at all it may appear to affect the whole display. This canbe corrected by performing a gamma correction on the entire display.Thus, most or all visible traces of the artifact caused by touch sensingcan be removed.

Thus, according to embodiments of the invention, multi-touch sensing canbe performed at the same TFT substrate of an LCD display in whichdisplay related functions are performed. Furthermore, the touch sensingand display related functions can share much of the same circuitry. Thiscan greatly reduce the cost and improve the efficiency of multi-touchcapable displays.

A multi-touch capable display may be used in various devices. Thus,embodiments of this invention encompass but are not limited to devicessuch as cellular phones, portable music players, GPS devices, PDAs,portable email devices, electronic kiosks, computers, and other devicesutilizing multi-touch displays.

In the above discussed embodiments, references to ground or 0V canactually refer to a virtual ground voltage, even if that voltage is at adifferent value than 0V. Unless explicitly noted otherwise (e.g., byreferring to a “touch pixel”), the term “pixel” can refer to a displaypixel.

Although embodiments of the invention are described herein in terms ofin-plane switching LCD displays, it should be understood that theinvention is not limited to this type of display, but is generallyapplicable to other displays as well.

Although the invention has been fully described in connection withembodiments thereof with reference to the accompanying drawings, it isto be noted that various changes and modifications will become apparentto those skilled in the art. Such changes and modifications are to beunderstood as being included within the scope of the invention asdefined by the appended claims.

What is claimed is:
 1. A display device configured for operation in adisplay mode and a touch mode, the device comprising: at least onedisplay pixel having a data line configured to transmit a display datasignal in the display mode and a stimulation signal in the touch mode;and a switch configured to switch the data line between the display modeand the touch mode.
 2. The display device of claim 1, wherein the atleast one display pixel comprises a first plurality of display pixels, aportion of the first plurality of display pixels sharing the same dataline, and wherein each display pixel of the first plurality of displaypixels has a data line configured to transmit a display data signal inthe display mode and a stimulation signal in the touch mode; and atleast for each display pixel in the portion of the first plurality ofdisplay pixels, the display device includes a switch configured toswitch the data line between the display mode and the touch mode.
 3. Thedisplay device of claim 2, further comprising a plurality of counterdata lines coupled to the first plurality of display pixels during thetouch mode.
 4. The display device of claim 3, wherein each display pixelof the first plurality of display pixels has a first electrode and asecond electrode, the first electrode coupled to the corresponding dataline and the second electrode coupled to one of the plurality of counterdata lines during the touch mode.
 5. The display device of claim 4,wherein the stimulation signal is coupled to the counter data linesduring the touch mode.
 6. The display device of claim 1, furthercomprising a first counter data line coupled to the at least one displaypixel during the touch mode.
 7. The display device of claim 6, whereinthe at least one display pixel has a first electrode and a secondelectrode, the first electrode coupled to the data line and the secondelectrode coupled to the first counter data line.
 8. The display deviceof claim 7, wherein the at least one display pixel comprises a touchstimulus pixel and the device further comprising at least one chargesensor pixel and wherein the at charge sensor pixel has a data lineconfigured to transmit another display data signal in the display modeand is coupled to capacitance sensing circuitry in the touch mode. 9.The display device of claim 8, further comprising a second counter dataline and wherein the second counter data line is coupled to the chargesensor pixel during the touch mode.
 10. The display device of claim 9,wherein charge sensor pixel has a first and second electrode, the firstelectrode coupled the data line of the charge sensor pixel and thesecond electrode coupled to the second counter data line during thetouch mode.
 11. The display device of claim 10, wherein the firstelectrode of the touch stimulus pixel is coupled to the data line of thetouch stimulus pixel and the second electrode is coupled to the secondcounter data line.
 12. The display device of claim 1, wherein the atleast one display pixel comprises a touch stimulus pixel and the devicefurther comprising at least one charge sensor pixel and wherein the atcharge sensor pixel has a data line configured to transmit anotherdisplay data signal in the display mode and is coupled to capacitancesensing circuitry in the touch mode.
 13. A display device configured foroperation in a display mode and a touch mode, the device comprising: atleast one touch stimulus pixel having a data line configured to transmita display data signal in the display mode and a stimulation signal inthe touch mode; at least one charge sensor pixel having a data lineconfigured to transmit another display data signal in the display modeand being coupled to capacitance sensing circuitry in the touch mode;and a switch configured to switch the data line between the display modeand the touch mode.
 14. The display device of claim 13, wherein thetouch stimulus pixel has first electrode and a second electrode, thefirst electrode coupled to the data line of the touch stimulus pixel andthe second electrode coupled to a first counter data line, the firstcounter data line coupled to transmit the stimulation signal in thetouch mode.
 15. The display device of claim 14, wherein the chargesensor pixel has first electrode and a second electrode, the firstelectrode coupled to the data line of the charge sensor pixel and thesecond electrode coupled to a second counter data line, the secondcounter data line coupled to the capacitance sensing circuitry in thetouch mode.
 16. The display device of claim 13, wherein the chargesensor pixel has first electrode and a second electrode, the firstelectrode coupled to the data line of the charge sensor pixel and thesecond electrode coupled to a counter data line, the counter data linecoupled to the capacitance sensing circuitry in the touch mode.
 17. Thedisplay device of claim 13, wherein the touch stimulus pixel has firstelectrode and a second electrode, the first electrode coupled to thedata line of the touch stimulus pixel and the second electrode coupledto a first counter data line, the first counter data line coupled totransmit another stimulation signal in the touch mode.
 18. The displaydevice of claim 17, wherein the charge sensor pixel has first electrodeand a second electrode, the first electrode coupled to the data line ofthe charge sensor pixel and the second electrode coupled to a secondcounter data line, the second counter data line coupled to thecapacitance sensing circuitry in the touch mode.
 19. The display deviceof claim 13, further comprising: at least one guard pixel placed betweenthe at least one touch stimulus pixel and the at least one charge sensorpixel, the at least one guard pixel having a data line configured totransmit yet another display data signal in the display mode and begincoupled to a predefined voltage during the touch mode.
 20. The displaydevice of claim 19, wherein the predefined voltage is a ground voltage.21. A display device configured for operation in a display mode and atouch mode, the device comprising: at least one display pixel having adata line configured to transmit a display data signal in the displaymode and a being coupled to capacitance sensing circuitry in the touchmode; and a switch configured to switch the data line between thedisplay mode and the touch mode.
 22. The display device of claim 21,wherein the at least one display pixel comprises a first plurality ofdisplay pixels, a portion of the first plurality of display pixelssharing the same data line, and wherein each display pixel of the firstplurality of display pixels has a data line configured to transmit adisplay data signal in the display mode and being coupled to thecapacitance sensing circuitry in the touch mode; and at least for eachdisplay pixel in the portion of the first plurality of display pixels,the display device includes a switch configured to switch the data linebetween the display mode and the touch mode.
 23. The display device ofclaim 22, further comprising a plurality of counter data lines coupledto the first plurality of display pixels during the touch mode.
 24. Thedisplay device of claim 23, wherein each display pixel of the firstplurality of display pixels has a first electrode and a secondelectrode, the first electrode coupled to the corresponding data lineand the second electrode coupled to one of the plurality of counter datalines.
 25. A display device configured for operation in a display modeand a touch mode, the device comprising: a plurality of touch stimuluspixels having data lines configured to transmit first display datasignals in the display mode and stimulation signals in the touch mode; aplurality of charge sensor pixels having data lines configured totransmit display second data signals in the display mode and beingcoupled to capacitance sensing circuitry in the touch mode; and a switchconfigured to switch the data line between the display mode and thetouch mode.
 26. The display device of claim 25, wherein the plurality oftouch stimulus pixels are disposed in a two dimensional array and theplurality of charge sensor pixels are disposed in a two dimension arrayadjacent the plurality of touch stimulus pixels.
 27. The display deviceof claim 26, further comprising a plurality of guard pixels, theplurality of guard pixels disposed in a two dimensional array andpositioned between the plurality of touch stimulus pixels and theplurality of charge sensor pixels.
 28. A display and touch sensingmethod using a display having at least one touch stimulus pixel and atleast one charge sensor pixel, the method comprising: transmitting afirst display data signal on a data line of the at least one touchstimulus pixel in a display mode; transmitting a first stimulationsignal on the data line of the at least one touch stimulus pixel in atouch mode; transmitting a second display data signal on a data line ofthe at least one charge sensor pixel in the display mode; coupling thedata line of the at least one charge sensor pixel to capacitancemeasuring circuitry in the touch mode; and switching the data lines ofthe at least one touch stimulus pixel and the at least one charge sensorpixel between the display mode and the touch mode.
 29. The method ofclaim 28, wherein the touch stimulus pixel has a first and secondelectrode and the method further comprises: coupling the first electrodeto the data line of the touch stimulus pixel in the display mode;coupling the second electrode to a first counter data line; and couplingthe first counter data line to the stimulation signal in the touch mode.30. The method of claim 29, wherein the charge sensor pixel has a firstand second electrode and the method further comprises: coupling thefirst electrode to the data line of the charge sensor pixel in thedisplay mode; coupling the second electrode to a second counter dataline; and coupling the second counter data line to the capacitancemeasuring circuitry in the touch mode.